1. Field of the Invention
The present invention relates to a friction couple that can suppress variations in a friction force.
2. Description of the Related Art
Friction members according to the related art for use as a sliding member for clutches or brakes for automobiles, machine tools, and so forth contain a thermosetting resin, such as a phenol resin, as a binder. The thermosetting resin is occasionally decomposed or melted into low-molecular materials when it is subjected to friction, which adversely affects the noise and vibration characteristics of the friction member.
A friction member that contains a polyimide resin in place of the thermosetting resin that is described above is disclosed. Japanese Patent Publication No. 5-62916 discloses a polyimide-based friction member obtained by thermocompression molding of a polyimide-based composition that has an aromatic polyimide resin.
The friction member which contains a polyimide resin disclosed in Japanese Patent Publication No. 5-62916 has excellent heat resistance. When the temperature exceeds a level at which the resin is decomposed during a braking operation under a high load, however, a low-molecular gas may be produced during decomposition and temporarily press back a brake pad or the like to reduce the friction coefficient, which causes a so-called “brake fade”. The polyimide-based composition disclosed in Japanese Patent Publication No. 5-62916, or specifically its aromatic polyimide resin powder, contains fluorine resin powder, which is occasionally used as a lubricant. Because of the brake fade due to the polyimide resin and the low friction coefficient of the fluorine resin, it is considered to be difficult to suppress a reduction in the friction coefficient during the occurrence of the brake fade.